Chapter 1 Notes - Chapter 1 Principles of Perceptual...

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Chapter 1: Principles of Perceptual Measurement Sensory process : Captures information from the physical world and transforms them into biological processes Perception : A single unified awareness of a stimulus that in turn arises from the sensation produced by our sensory systems Perception is a very private experience and cannot be measured by anyone else. But we can measure our own perception! A. Scientific Basis of Perceptual Measurement To learn about perception, you need to measure two variables: 1) Physical Stimulus 2) The resulting perceptual impression Understanding the relationships between the two has many benefits: 1) Provides an estimate of the perceptual quality of a stimulus in numerical terms and allows for comparisons with other stimuli. So a market can see how well the public reacts to a new perfume. 2) Allows for comparisons between humans or even species 3) Allows comparing of different sensory modalities (cross-modal comparison) Two approaches to understand the relationship between the physical stimulus intensity and the perceptual experience: 1) Ask human subjects to rate the perceived intensity 2) Measure the smallest change in stimulus needed to cause a change in sensation To plot the mathematical relationship between the two, you need the starting point and the slope B. Classical Psychophysics Absolute threshold : the intensity needed before the brain could register a sensory event Sub-threshold : Stimulus below the threshold level Supra-threshold : region where sensation is taking place Difference threshold : How small a change in stimulus intensity is required to produce a discriminable change in sensation Gustav Fechner: (1801-1887) 1
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Father of psychophysics Wanted to determine the relationship between mind and body Believed that thresholds represented fundamental parameters in the grand formula or perception Came up with three methods to obtain absolute and difference threshold 1) Method of Adjustment: adjust the stimulus intensity until it’s not noticeable 2) Method of Limits: more preferable because this technique provides more reliable estimates. The subject is presented with a stimulus whose intensity is chosen from an ascending or descending series. If ascending, the intensity of the stimulus is initially set at a sub threshold value and increased by a fixed amount in successive trials until the subject reports that it is perceived. The transition provides a reasonable estimate of the threshold 3) Method of Constant Stimuli: The values are randomly chosen and presented to the subject and the subject only has to say whether he felt a sensation or not. One problem with this method is choosing the range of stimulus. Optimally, the threshold should be somewhere in the middle of this range.
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